1. Field of the Invention
The present invention relates to a silencer shell forming apparatus.
2. Description of the Related Art
Conventionally, shells used for silencers of internal combustion engines have been made by forming a metal sheet such as a stainless sheet and the like into a cylindrical shape having an elliptical section, oval section or the like.
An example of a manufacturing process of the silencer shell will be schematically described with reference to FIG. 9. A raw material 101 is fed by a raw material feeder until it is abutted against a stopper 103 below a mandrel 102 as shown at step No. 1; at step No. 2, presser plates 104 located at both the sides of the mandrel 102 are lifted to thereby cause the raw material 101 to be wound around the lower half of the mandrel 102 as well as both the end portions 105 of the raw material 101 to be raised; at step No. 3, the edges of both the end portions 105 of the raw material 101 are bent by bending rollers 106 disposed at the extreme end of a roll carriage in the advancing direction, that is, to the extreme end of the moving direction of the roll carriage; at step No. 4, both the end portions 105 are bent inward by forming bars 107; at step No. 5, both the end portions 105 are sequentially rolled in and subjected to lock seaming as the forming rollers 108 of the roll carriage, which are disposed along the axial direction of the mandrel 102, move forward to thereby form a shell 109; thereafter, the shell 109 having been formed into a cylindrical shape is removed from the mandrel 102.
JP-B2-07-32943 discloses a mandrel illustrated in FIG. 10 showing prior art (which is a first prior art in this description) as the mandrel used in the above forming apparatus. Further, JP-U-04-104237 discloses a mandrel illustrated in FIG. 11 (which is a second prior art in this description).
The first prior art shown in FIG. 10 is arranged such that a mandrel 201 is divided into two segments 202 and 203 in a right and left direction and they are mounted to a holder 204 from the outside thereof. The segment 202 is moved in the right and left direction by a hydraulic cylinder 205 provided with the holder 204 so that the outer peripheral length of the mandrel 201 can be varied.
The second prior art shown in FIG. 11 is arranged such that a mandrel 301 is divided into two segments in an up and down direction and the upper segment 302 is mounted to the outer periphery of a mandrel bar 303 and fixed thereto, the lower segment 304 is upward and downward movably disposed below the upper segment 302 and the lower segment 304 is moved upward and downward by an hydraulic cylinder 305 incorporated in the mandrel bar 303 so that the outer peripheral length of the mandrel 301 can be varied.
In the above prior arts, a shell is formed in such a manner that a raw material is tightly wound around the mandrel in a state that the segments are expanded and the shell is removed from the mandrel after it has been formed. Thus, an object of the prior art is to easily remove the shell from the mandrel by reducing the outer peripheral length of the mandrel by moving one of the segments in the contracting direction of the mandrel so as to form an interval between the mandrel and the shell. As a result, in this case, it suffices for one of the segments to move only in a very small distance of, for example, a few millimeters.
Incidentally, since there are various types of silencers having different capacities, shells are formed to have different outer peripheral lengths.
In the above prior art, however, the segment of the mandrel does not move a distance enough to form different types of shells, although it moves slightly. Further, since the hydraulic cylinder is disposed in the radial direction of the mandrel and moves only one of the segments, the hydraulic cylinder has a limited stroke in a narrow space and cannot greatly vary the outer peripheral length of the mandrel. Thus, the prior art cannot form the different types of the shells from the structure thereof.
Accordingly, when a shell having a different outer peripheral length is formed, a mandrel being used must be replaced with another mandrel dedicated for the shell having a different section. Thus, the previously used mandrel must be removed and a job for assembling the new mandrel is required as well as when the right to left diameter of the mandrel is varied by the replacement, the interval between presser plates for winding a raw material around the mandrel must be adjusted, by which a problem arises in that a job for changing setup is needed, an idle time is made, productivity is lowered and a manufacturing cost is increased.